Studies on the Relationships Between Earthworms and Soil Fertility

The rate of cocoon production in British Lumbricidae differs considerably from species to species and is greatly affected by soil temperature, moisture and the food supply of the adult worms. Only two out of fourteen species studied frequently produced more than one worm per cocoon, and twins were only recorded once in many hundreds of observations on four species of the genus Lumbricus.
The incubation period of the cocoons and the growth period to sexual maturity varies from species to species and also depends on the time of year at which the cocoons are deposited and the young worms emerge.